Texture Coordinate Gradients Estimation for Ray Cones

Abstract

Ray cones were presented as a fast, approximate way to calculate a suitable mip level index for a particular texture sample in a ray tracing shader setup. Though the original technique was doing all the mathematics needed to compute the final mip level index, in this chapter we reformulate the problem in a different way that relies on existing hardware-supported instructions. This maintains almost the same visual results and leads to more convenient shader code. It also further simplifies and reduces the number of instructions from the original ray cones implementation, though we do not claim this necessarily leads to better performance.